This invention pertains generally to inertial reference systems and particularly to an inertial roll attitude reference system for a spinning projectile.
A guidance system for a spinning projectile is described in U.S. Pat. No. 4,347,996 issued Sept. 7, 1982 to V. A. Grosso and assigned to the same assignee as this application. In that system, advantage is taken of the spin-induced angular momentum vector in a spinning projectile to measure the angle between the line-of-sight between such projectile and a selected target and the velocity vector of such projectile (and the first derivative of such angle). In accordance with the teaching of the just-cited patent, a body-fixed seeker is used to derive control signals for guiding the projectile toward a selected target. In operation it is necessary that a "roll reference" be provided to determine the relationship between the plane (referred to as the "engagement plane") determined by the velocity vector of the spinning projectile and the line-of-sight from such projectile to a selected target. That is to say, an "inertial roll reference" is required. In the system being discussed an inertial roll reference is provided by detecting the maxima and minima of signals from a ground based source of linearly polarized radiations illuminating a linearly polarized antenna affixed to the spinning projectile. Obviously such an arrangement is feasible only in tactical situations wherein the linearly polarized antenna may be continuously illuminated during flight. In other tactical situations, for example when the target is beyond the horizon, it is evident that the requisite roll reference cannot be derived by illuminating an antenna so other means of deriving such reference must be provided. According to the known art, appropriate inertial instrumentation is the only way to derive a roll reference. However, as noted in the patent being discussed, the inertial instrumentation would have to include a gyroscope, meaning that the advantages of spin stabilization would be lost.